Investigation of an outbreak of Salmonella enterica serovar Newport infection

Outbreak of Salmonella Newport associated with internationally distributed raw goats' milk cheese, France, 2018

Raw milk cheeses are commonly consumed in France and are also a common source of foodborne outbreaks (FBOs). Both an FBO surveillance system and a laboratory-based surveillance system aim to detect Salmonella outbreaks. In early August 2018, five familial FBOs due to Salmonella spp. were reported to a regional health authority. Investigation identified common exposure to a raw goats' milk cheese, from which Salmonella spp. were also isolated, leading to an international product recall. Three weeks later, on 22 August, a national increase in Salmonella Newport ST118 was detected through laboratory surveillance. Concomitantly isolates from the earlier familial clusters were confirmed as S. Newport ST118. Interviews with a selection of the laboratory-identified cases revealed exposure to the same cheese, including exposure to batches not included in the previous recall, leading to an expansion of the recall. The outbreak affected 153 cases, including six cases in Scotland. S. Newport was detected in the cheese and in the milk of one of the producer's goats. The difference in the two alerts generated by this outbreak highlight the timeliness of the FBO system and the precision of the laboratory-based surveillance system. It is also a reminder of the risks associated with raw milk cheeses.

Microbial Contamination of Fresh Produce: What, Where, and How?

Promotion of healthier lifestyles has led to an increase in consumption of fresh produce. Such foodstuffs may expose consumers to increased risk of foodborne disease, as often they are not subjected to processing steps to ensure effective removal or inactivation of pathogenic microorganisms before consumption. Consequently, reports of ready-to-eat fruit and vegetable related disease outbreak occurrences have increased substantially in recent years, and information regarding these events is often not readily available. Identifying the nature and source of microbial contamination of these foodstuffs is critical for developing appropriate mitigation measures to be implemented by food producers. This review aimed to identify the foodstuffs most susceptible to microbial contamination and the microorganisms responsible for disease outbreaks from information available in peer-reviewed scientific publications. A total of 571 outbreaks were identified from 1980 to 2016, accounting for 72,855 infections and 173 deaths. Contaminated leafy green vegetables were responsible for 51.7% of reported outbreaks. Contaminated soft fruits caused 27.8% of infections. Pathogenic strains of Escherichia coli and Salmonella, norovirus, and hepatitis A accounted for the majority of cases. Large outbreaks resulted in particular biases such as the observation that contaminated sprouted plants caused 31.8% of deaths. Where known, contamination mainly occurred via contaminated seeds, water, and contaminated food handlers. There is a critical need for standardized datasets regarding all aspects of disease outbreaks, including how foodstuffs are contaminated with pathogenic microorganisms. Providing food business operators with this knowledge will allow them to implement better strategies to improve safety and quality of fresh produce.

Complete Genome Sequence of Salmonella enterica Serovar Newport Myophage Melville

Multiple antimicrobial-resistant strains of Salmonella enterica serovar Newport have been recorded. Study on phages infecting S. Newport may provide new therapeutics or diagnostics for this pathogen.

Multiple antimicrobial-resistant strains of Salmonella enterica serovar Newport have been recorded. Study on phages infecting S. Newport may provide new therapeutics or diagnostics for this pathogen. Here, we describe the complete genome sequence of the T4-like phage Melville that uses S. Newport as one of its hosts.

The Hurdle Approach-A Holistic Concept for Controlling Food Safety Risks Associated With Pathogenic Bacterial Contamination of Leafy Green Vegetables. A Review

Consumers appreciate leafy green vegetables such as baby leaves for their convenience and wholesomeness and for adding a variety of tastes and colors to their plate. In Western cuisine, leafy green vegetables are usually eaten fresh and raw, with no step in the long chain from seed to consumption where potentially harmful microorganisms could be completely eliminated, e.g., through heating. A concerning trend in recent years is disease outbreaks caused by various leafy vegetable crops and one of the most important foodborne pathogens in this context is Shiga toxin-producing Escherichia coli (STEC). Other pathogens such as Salmonella, Shigella, Yersinia enterocolitica and Listeria monocytogenes should also be considered in disease risk analysis, as they have been implicated in outbreaks associated with leafy greens. These pathogens may enter the horticultural value network during primary production in field or greenhouse via irrigation, at harvest, during processing and distribution or in the home kitchen/restaurant. The hurdle approach involves combining several mitigating approaches, each of which is insufficient on its own, to control or even eliminate pathogens in food products. Since the food chain system for leafy green vegetables contains no absolute kill step for pathogens, use of hurdles at critical points could enable control of pathogens that pose a human health risk. Hurdles should be combined so as to decrease the risk due to pathogenic microbes and also to improve microbial stability, shelf-life, nutritional properties and sensory quality of leafy vegetables. The hurdle toolbox includes different options, such as physical, physiochemical and microbial hurdles. The goal for leafy green vegetables is multi-target preservation through intelligently applied hurdles. This review describes hurdles that could be used for leafy green vegetables and their biological basis, and identifies prospective hurdles that need attention in future research.

Enzymatic Digestion for Improved Bacteria Separation from Leafy Green Vegetables

An effective and rapid method for the separation of bacteria from food matrix remains a bottleneck for rapid bacteria detection for food safety. Bacteria can strongly attach to a food surface or internalize within the matrix, making their isolation extremely difficult. Traditional methods of separating bacteria from food routinely involve stomaching, blending, and shaking. However, these methods may not be efficient at removing all the bacteria from complex matrices. Here, we investigate the benefits of using enzyme digestion followed by immunomagnetic separation to isolate Salmonella from spinach and lettuce. Enzymatic digestion using pectinase and cellulase was able to break down the structure of the leafy green vegetables, resulting in the detachment and release of Salmonella from the leaves. Immunomagnetic separation of Salmonella from the liquefied sample allowed an additional separation step to achieve a more pure sample without leaf debris that may benefit additional downstream applications. We have investigated the optimal combination of pectinase and cellulase for the digestion of spinach and lettuce to improve sample detection yields. The concentrations of enzymes used to digest the leaves were confirmed to have no significant effect on the viability of the inoculated Salmonella. Results reported that the recovery of the Salmonella from the produce after enzyme digestion of the leaves was significantly higher (P < 0.05) than traditional sample preparation methods to separate bacteria (stomaching and manually shaking). The results demonstrate the potential for use of enzyme digestion prior to separation can improve the efficiency of bacteria separation and increase the likelihood of detecting pathogens in the final detection assay.

Salmonellosis associated with mass catering: a survey of European Union cases over a 15-year period

Salmonella spp. is the causative agent of a foodborne disease called salmonellosis, which is the second most commonly reported gastrointestinal infection in the European Union (EU). Although over the years the annual number of cases of foodborne salmonellosis within the EU has decreased markedly, in 2014, a total of 88 715 confirmed cases were still reported by 28 EU Member States. The European Food Safety Authority reported that, after the household environment, the most frequent settings for the transmission of infection were catering services. As evidenced by the reviewed literature, which was published over the last 15 years (2000-2014), the most frequently reported causative agents were Salmonella Enteritidis and Salmonella Typhimurium serovars. These studies on outbreaks indicated the involvement of various facilities, including hospital restaurants, takeaways, ethnic restaurants, hotels, in-flight catering, one fast-food outlet and the restaurant of an amusement park. The most commonly reported sources of infection were eggs and/or egg-containing foods, followed by meat- and vegetable-based preparations. Epidemiological and microbiological studies allowed common risk factors to be identified, including the occurrence of cross-contamination between heat-treated foods and raw materials or improperly cleaned food-contact surfaces.

Biosurfactant Produced by Salmonella Enteritidis SE86 Can Increase Adherence and Resistance to Sanitizers on Lettuce Leaves (Lactuca sativa L., cichoraceae)

Salmonella Enteritidis SE86 is an important foodborne pathogen in Southern Brazil and it is able to produce a biosurfactant. However, the importance of this compound for the microorganism is still unknown. This study aimed to investigate the influence of the biosurfactant produced by S. Enteritidis SE86 on adherence to slices of lettuce leaves and on resistance to sanitizers. First, lettuce leaves were inoculated with S. Enteritidis SE86 in order to determine the amount of biosurfactant produced. Subsequently, lettuce leaves were inoculated with S. Enteritidis SE86 with and without the biosurfactant, and the adherence and bacterial resistance to different sanitization methods were evaluated. S. Enteritidis SE86 produced biosurfactant after 16 h (emulsification index of 11 to 52.15 percent, P < 0.05) and showed greater adherence capability and resistance to sanitization methods when the compound was present. The scanning electron microscopy demonstrated that S. Enteritidis was able to adhere, form lumps, and invade the lettuce leaves' stomata in the presence of the biosurfactant. Results indicated that the biosurfactant produced by S. Enteritidis SE86 contributed to adherence and increased resistance to sanitizers when the microorganism was present on lettuce leaves.

Are ready-to-eat salads ready to eat? An outbreak of Salmonella Coeln linked to imported, mixed, pre-washed and bagged salad, Norway, November 2013

We investigated a nationwide outbreak of Salmonella Coeln in Norway, including 26 cases identified between 20 October 2013 and 4 January 2014. We performed a matched case-control study, environmental investigation and detailed traceback of food purchases to identify the source of the outbreak. In the case-control study, cases were found to be more likely than controls to have consumed a ready-to-eat salad mix (matched odds ratio 20, 95% confidence interval 2·7-∞). By traceback of purchases one brand of ready-to-eat salad was indicated, but all environmental samples were negative for Salmonella. This outbreak underlines that pre-washed and bagged salads carry a risk of infection despite thorough cleaning procedures by the importer. To further reduce the risk of infection by consumption of ready-to-eat salads product quality should be ensured by importers. Outbreaks linked to salads reinforce the importance of implementation of appropriate food safety management systems, including good practices in lettuce production.

An Outbreak of Cryptosporidium parvum across England & Scotland Associated with Consumption of Fresh Pre-Cut Salad Leaves, May 2012

BACKGROUND

We report a widespread foodborne outbreak of Cryptosporidium parvum in England and Scotland in May 2012. Cases were more common in female adults, and had no history of foreign travel. Over 300 excess cases were identified during the period of the outbreak. Speciation and microbiological typing revealed the outbreak strain to be C. parvum gp60 subtype IIaA15G2R1.

METHODS

Hypothesis generation questionnaires were administered and an unmatched case control study was undertaken to test the hypotheses raised. Cases and controls were interviewed by telephone. Controls were selected using sequential digit dialling. Information was gathered on demographics, foods consumed and retailers where foods were purchased.

RESULTS

Seventy-four laboratory confirmed cases and 74 controls were included in analyses. Infection was found to be strongly associated with the consumption of pre-cut mixed salad leaves sold by a single retailer. This is the largest documented outbreak of cryptosporidiosis attributed to a food vehicle.

Timeliness of epidemiological outbreak investigations in peer-reviewed European publications, January 2003 to August 2013

Binary file ES_Abstracts_Final_ECDC.txt matches

An outbreak of Salmonella Newport associated with mung bean sprouts in Germany and the Netherlands, October to November 2011

Binary file ES_Abstracts_Final_ECDC.txt matches

Prevalence, serovars, and antimicrobial susceptibility of Salmonella isolated from blue land crabs (Cardisoma guanhumi) in Grenada, West Indies

Samples of intestine and hepatopancreas from 65 blue land crabs (Cardisoma guanhumi), a crustacean commonly consumed as a food item in Grenada, were collected from six geographic sites in Grenada and tested for Salmonella by enrichment and selective culture. The individual animal prevalence of Salmonella based on isolation was 17% (11 of 65), and all infected crabs were from three of the six sampled locations. Isolates were identified by serotyping as Salmonella enterica serovars Saintpaul (n = 6), Montevideo (n = 4), and Newport (n = 1). The intestines of all 11 infected crabs were positive for Salmonella, but only 7 of 11 hepatopancreas samples were positive for Salmonella, and these isolates were the same serovar as isolated from the matching intestine. These three Salmonella serovars are known to cause human illness in many countries, and in the Caribbean Salmonella Saintpaul has been frequently isolated from humans. In a disc diffusion assay, all isolates were susceptible to all 11 drugs tested: amoxicillin-clavulanic acid, ampicillin, cephalothin, chloramphenicol, ciprofloxacin, gentamicin, imipenem, neomycin, streptomycin, tetracycline, and trimethoprim-sulfamethoxazole. To our knowledge, this report is the first concerning isolation and antimicrobial susceptibilities of Salmonella serotypes from the blue land crab.

National outbreaks of Salmonella infection in the UK, 2000–2011

Over a 12-year period, the Health Protection Agency's (now Public Health England's) Department of Gastrointestinal and Emerging Infections (GEZI) investigated over 100 potential national outbreaks of Salmonella enterica. These ranged from a cluster of cases requiring data interrogation and monitoring of the situation, to full blown case-control studies involving hundreds of interviews, many staff, multi-agency collaboration and the media. Vehicles of infection ranged from the usual suspects of chicken and eggs, to the less frequently implicated snake feed and chocolate. This has forced us to alter our preconceptions of disease transmission. The way in which GEZI investigate outbreaks and conduct case-control studies is constantly evolving as we learn and adapt to the changing aetiology of S. enterica. We present the findings and lessons learned during the last 12 years of investigating S. enterica outbreaks in England and Wales.

Salmonella, a cross-kingdom pathogen infecting humans and plants

Infections with non-typhoidal Salmonella strains are constant and are a non-negligible threat to the human population. In the last two decades, salmonellosis outbreaks have increasingly been associated with infected fruits and vegetables. For a long time, Salmonellae were assumed to survive on plants after a more or less accidental infection. However, this notion has recently been challenged. Studies on the infection mechanism in vegetal hosts, as well as on plant immune systems, revealed an active infection process resembling in certain features the infection in animals. On one hand, Salmonella requires the type III secretion systems to effectively infect plants and to suppress their resistance mechanisms. On the other hand, plants recognize these bacteria and react to the infection with an induced defense mechanism similar to the reaction to other plant pathogens. In this review, we present the newest reports on the interaction between Salmonellae and plants. We discuss the possible ways used by these bacteria to infect plants as well as the plant responses to the infection. The recent findings indicate that plants play a central role in the dissemination of Salmonella within the ecosystem.

Identification of Salmonella enterica genes with a role in persistence on lettuce leaves during cold storage by recombinase-based in vivo expression technology

Recurrent outbreaks of enteric illness linked to lettuce and a lack of efficacious strategies to decontaminate produce underscores the need for a better understanding of the molecular interactions of foodborne pathogens with plants. This study aimed at identifying Salmonella enterica genes involved in the persistence of this organism on post-harvest lettuce during cold storage using recombinase-based in vivo expression technology (RIVET). In total, 37 potentially induced loci were identified in four distinct screenings. Knockout mutations in eight upregulated genes revealed that four of them have a role in persistence of the pathogen in this system. These genes included stfC, bcsA, misL, and yidR, encoding a fimbrial outer membrane usher, a cellulose synthase catalytic subunit, an adhesin of the autotransporter family expressed from the Salmonella pathogenicity island-3, and a putative ATP/GTP-binding protein, respectively. bcsA, misL, and yidR but not stfC mutants were impaired also in attachment and biofilm formation, suggesting that these functions are required for survival of S. enterica on post-harvest lettuce. This is the first report that MisL, which has a role in Salmonella binding to fibronectin in animal hosts, is involved also in adhesion to plant tissue. Hence, our study uncovered a new plant attachment factor in Salmonella and demonstrates that RIVET is an effective approach for investigating human pathogen-plant interactions in a post-harvest leafy vegetable.

The "case-chaos study" as an adjunct or alternative to conventional case-control study methodology

Case-control studies are important in infectious disease epidemiology for rapidly identifying and controlling risks, but challenges, including the need for speed, can place practical restrictions on control selection and recruitment. The biased comparisons that result can hamper or, worse, mislead investigators. Following a 2009 outbreak of Shiga-like toxin-producing Escherichia coli O157 infection associated with a petting farm in southeast England, it was hypothesized that case behavior alone could be used to identify risks. Case-patients' exposures were randomized on a case-by-case basis, and the resulting permuted data were compared with the actual events preceding illness by conditional logistic regression analysis. There was good agreement between the risks identified by using our new method and the risks elicited in the original outbreak case-control studies. This was also the case in analysis of 2 further historical outbreaks. These initial findings suggest that the technique, which we have called the "case-chaos" technique, appeared to be useful in this setting. Analysis of simulated data supports this view. Circumventing the need for traditional control data has the potential to reduce outbreak investigation lead times, leading to earlier interventions and reduced morbidity and mortality. However, further validation is necessary, coupled with an awareness of limitations of the method.

X-Ray Irradiation as a Microbial Intervention Strategy for Food

First recognized in 1895, X-ray irradiation soon became a breakthrough diagnostic tool for the dental and medical professions. However, the food industry remained slow to adopt X-ray irradiation as a means for controlling insects and microbial contaminants in food, instead using gamma and electron beam (E-beam) irradiation. However, the reinvention of X-ray machines with increased efficiency, combined with recent developments in legislation and engineering, is now allowing X-ray to actively compete with gamma irradiation and E-beam as a microbial reduction strategy for foods. This review summarizes the historical developments of X-rays and discusses the key technological advances over the past two decades that now have led to the development of several different X-ray irradiators capable of enhancing the safety and shelf life of many heat-sensitive products, including lettuce, spinach, tomatoes, and raw almonds, all of which have been linked to high profile outbreaks of foodborne illness.

Pathogenic potential of Salmonella Typhimurium DT104 following sequential passage through soil, packaged fresh-cut lettuce and a model gastrointestinal tract

From a quantitative microbial risk assessment perspective it is important to know whether certain food environments influence the pathogenic potential of pathogens and to what extent. The purpose of the present study was to examine the pathogenic potential of S. Typhimurium DT104, measured as the capability to survive a simulated gastrointestinal tract system and the capability of adhering to and invading differentiated Caco-2 cells, after sequential incubation (without intermediate culturing) into soil, lettuce and cut lettuce stored under modified atmosphere (MAP) conditions. Two S. Typhimurium DT104 strains were used, one isolated from a pig carcass and one isolated from lettuce. The most important result of the present study is that the sequential incubation of S. Typhimurium in soil and lettuce slightly increased the capability of surviving the simulated gastric fluid, increased the capability to grow in the simulated intestinal fluid but decreased the capability of epithelial attachment and invasion and decreased the overall survival probability of the gastrointestinal tract system. Some variation in responses between the strains was observed, with the lettuce strain maintaining higher epithelial attachment capability and the carcass strains maintaining higher epithelial invasion capability. This study provided quantitative data on the effect of environmental and food matrices on the pathogenic potential of S. Typhimurium DT104 using a realistic system of sequential incubations in environmental and food matrices, followed by simulated gastrointestinal tract passage without intermediate culturing. These results could aid the development of more realistic quantitative microbial risk assessments.

Iceberg lettuce as suggested source of a nationwide outbreak caused by two Salmonella serotypes, Newport and Reading, in Finland in 2008

A nationwide outbreak of Salmonella enterica serotypes Newport and Reading occurred between 17 October and 28 November 2008 in Finland. A total of 77 culture-confirmed Salmonella Newport and 30 Salmonella Reading cases, including one case with a double infection, were reported. All strains isolated from the patients were subtyped using serotyping, microbial resistance profiling, and pulsed-field gel electrophoresis (PFGE). Here, the PFGE patterns of the studied Salmonella Newport strains were identical, whereas four different PFGE profiles were found among the Salmonella Reading strains. Two elderly patients died within 2 weeks of the onset of symptoms. Three geographical clusters of cases with an epidemiological link were identified. The traceback investigation suggested that the factor connecting the cases was ready-chopped iceberg lettuce available for mass catering use. However, none of the tested food, environmental samples, or the samples taken from the staff of the processing plant contained Salmonella bacteria. Tracing back to outbreak sources with a short shelf life can be complex.

A Salmonella Typhimurium phage type (PT) U320 outbreak in England, 2008: continuation of a trend involving ready-to-eat products

In March 2008, the Health Protection Agency in England conducted a retrospective case-control study to investigate the cause of 179 cases of the newly recognized, fully antimicrobial-sensitive Salmonella Typhimurium PT U320. Forty-three symptomatic laboratory-confirmed case-patients and 84 asymptomatic location-matched controls were interviewed by telephone about exposures in the 3 days prior to illness or interview. Multivariate logistic analysis indicated consumption of pre-packaged egg sandwiches (odds ratio 3·29, 95% confidence interval 1·19–9·09) was independently associated with illness. Eight of the 15 case-patients who consumed egg sandwiches did so from retail chain A (53·3%) whereas none of the eight controls consumed similar sandwiches (χ2=7·20, P⩽0·01). A review of the pre-packaged egg sandwich ingredients suggested this outbreak was probably caused by exposure to an ingredient common to pre-packaged sandwiches and prepared salads but we established a definitive epidemiological link with only the former. Short shelf-life, product diversity and investigation lag hinder epidemiological investigations of such popular products, providing continued challenges for food safety enforcement of freshly prepared produce.